Since the invention of the integrated circuit (IC), the semiconductor industry has experienced rapid growth due to continuous improvements in the integration density of various electronic components (i.e., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size, which allows more components to be integrated into a given area.
These integration improvements are essentially two-dimensional (2D) in nature, in that the volume occupied by the integrated components is essentially on the surface of the semiconductor wafer. Although dramatic improvement in lithography has resulted in considerable improvement in 2D IC formation, there are physical limits to the density that can be achieved in two dimensions. One of these limits is the minimum size needed to make these components. Also, when more devices are put into one chip, more complex designs are required.
In an attempt to further increase circuit density, three-dimensional (3D) ICs have been investigated. In a typical formation process of a 3D IC, two dies are bonded together and electrical connections are formed between each die and contact pads on a substrate. Interposer stacking is part of 3D IC technology, where a Through-Silicon-Via (TSV) embedded interposer is connected to a device silicon with a micro bump. 3D IC manufacturing process flows can be separated into two types. In a chip-on-chip-on-substrate (CoCoS) process flow, a silicon interposer chip is first attached onto a packaging substrate, and then a different device silicon chips is attached onto the interposer. In a chip-on-wafer-on-substrate (CoWoS) process flow, a device silicon chip is first attached onto a silicon interposer wafer, which is then diced. The resulting stacked silicon is then attached onto a substrate.